Method for preparing mutual dispersions of carbides and metals or alloys and novel products thereof

ABSTRACT

A MIXED OXIDE, A CO-PRECIPITATE OF HYDROXIDES OR A MIXED COMPLEX OF A FIRST METAL PROVIDING THE CARBIDE OF THE DISPERSION AND OF A SECOND METAL PROVIDING THE METAL OF THE DISPERSION ARE SUBJECTED TO A HEAT TREATMENT IN AN ENCLOSURE. THE COMPOUND THUS OBTAINED IS SUBJECTED, IN A REDUCING AND CARBURIZING ATMOSPHERE CONTAINING HYDROGEN AND METHANE, TO THERMAL TREATMENT BELOW 1100*C. TO REDUCE ALL THE OXIDES AND CARBURIZE THE FIRST METAL. HEATING IS EFFECTED AT A SPEED OF 100 TO 400*C./HOUR. THE DISPERSIONS COMPRISES PARTICLES OF SINGLE OR MIXED CARBIDES UNIFORMLY DISTRIBUTED IN THE MIDST OF ELEMENTARY GRAINS OF METAL. THE DISPRSIONS ARE USED IN POWDER METALLURGY.

R. A. PARIS ET AL 3,732,091

Mav 8, 1973 METHOD FOR PREPARING MUTUAL DISPERSIONS OF CARBIDES ANDMETALS OR ALLOYS AND NOVEL PRODUCTS THEREOF Filed July 1, 1970 INVENTO-RS ATTORN EY United States Patent Ofice 3,732,091 METHOD FORPREPARING MUTUAL DISPER- SION S F CARBIDES AND METALS 0R ALLOYS ANDNOVEL PRODUCTS THEREOF Ren A. Paris and Dominique Thibaudon, Lyon, MarcP. Roubin, Villeurbanne, and Jacques M. Paris, Lyon, France, assignorsto Agence Nationale de Valorisation de la Recherche (ANVAR), Puteaux,France Filed July 1, 1970, Ser. No. 51,470 Claims priority, applicationFrance, July 4, 1970, 6922753 Int. Cl. B22f 9/00 US. Cl. 75--.5 AC 9Claims ABSTRACT OF THE DISCLOSURE A mixed oxide, a co-precipitate ofhydroxides or a mixed complex of a first metal providing the carbide ofthe dispersion and of a second metal providing the metal of thedispersion are subjected to a heat treatment in an enclosure. Thecompound thus obtained is subjected, in a reducing and carburizingatmosphere containing hydrogen and methane, to thermal treatment below1100 C. to reduce all the oxides and carburize the first metal. Heatingis effected at a speed of 100 to 400 C./hour. The dispersions compriseparticles of single or mixed carbides uniformly distributed in the midstof elementary grains of metal. The dispersions are used in powdermetallurgy.

The invention relates to a method for the preparation of mutualdispersions of carbides and of metals or alloys, and to the productsthereof.

According as the metal or the carbide are preponderant in the dispersionconsidered, the description vw'll relate to a dispersion of carbide inthe metal or a dispersion of metal in carbide.

The dispersions of the first of these two categories have, with respectto the base metal or alloy, strengthened mechanical properties,particularly as regards hardness and resistance to flow, especially athigh temperature.

In dispersions of the second of the said categories, the metal serves asbinder between the grains of a powder of carbide intended for sintering.Of course, there is also produced an improvement in the mechanicalproperties of the sintered parts.

The invention relates also to dispersions of single or mixed carbides inmetals or alloys having characteristics which make them novel industrialproducts.

It is a particular object of the invention to make available to industrya method of preparation which is easy to put into practice and whichensures constant quality of the products obtained.

The method according to the invention is characterised in that,

In a first step, there is prepared a mixed oxide, a coprecipitate ofhydroxides or a mixed complex of a first metal (or several if it isdesired to obtain a mixed carbide) intended to provide the carbide ofthe dispersion and selected from among Ti, V, Nb, Ta and Cr and of asecond metal (or several if it is desired to obtain an alloy) intendedto provide the metal of the dispersion and selected from among Fe, Co,Ni, Cu, Zn, Cd, Ag, Sn, Pb, Bi, Ge and Tl, and

In a second step, the compound thus obtained is subjected, in the midstof an atmosphere both reducing and carburizing and comprising hydrogenand a hydrocarbon such as methane, to a heat treatment of which the tem-3,732,531 Patented May 8, 1973 perature (less than 1100 C.) and theduration are selected so that the reduction of all the oxides and thecarburation of the first metal are ensured, the heating being effectedpreferably at a speed of the order of 100 to 400 C./hour.

The dispersions according to the invention of carbides in metals arecharacterised in that they comprise particles of a single or mixedcarbide distributed uniformly in the midst of elementary grains of themetal or alloy selected.

In these products, the dimensions of the particles of the disperse phase(which are not concentrated at the junctions of grains of the metallicphase but distributed uniformly inside the latter) are of the order of 5to 500 III/1..

In the case of dispersions of a metal or alloy in a carbide, the metaloccurs localised at the junctions of the grains of carbide. Here again,the dimensions of the particles before sintering are of the order of 5to 500 mu.

When it is desired that the metallic phase be constituted by an alloy,there is employed a mixed oxide of metals of the second group.

In the case where the carbide of the second metal is stable under theconditions of simultaneous carburation and reduction, this step isfollowed by a supplementary treatment of reduction in pure hydrogen atthe same temperature for a time suificient to completely reduce thecarbide of the said second metal.

The method according to the invention may be applied in a fixed bed orin a fluidized bed.

According to the method selected, recourse may then be had respectivelyto an apparatus of the type of that shown diagrammatically in FIG. 1, orto an apparatus of the type of that shown diagrammatically in FIG. 2.

In the two cases, the hydrogen and the methane or other hydrocarbonarrive respectively through the pipes 1 and 2 opening into a single pipe3 which leads the gaseous mixture inside an enclosure 4 which is heatedby heating elements 5.

In the case of FIG. 1, the enclosure 4 is arranged horizontally and theproduct 6 to be treated is stacked in a thin layer in a container 7inside this enclosure. The treatment gas comes into contact with thesurface of the product 6.

In the case of FIG. 2, the enclosure is arranged vertically, the product6 forming a fiuid bed above the grid 8. This device also enables workingin a fixed bed, the treatment gas then passing through the layer ofproduct 6.

The apparatus of FIG. 2 enables the treatment of much larger amounts ofproduct 6 in shorter reaction times, Whether in a fixed bed or in afluid bed, since it achieves a better contact between the product 6 andthe treatment gas.

To establish ideas, it is indicated that the duration of the step ofsimultaneous reduction and carburation is (in the case of treatment in afixed bed by means of the apparatus of FIG. 1) generally of the order of10 to 20 hours.

The proportions of hydrogen and of hydrocarbon of the atmosphere usedduring this step are respectively of the order of 99.0 to and of 1 to10%. In practice, one adheres to approximately theoretical proportionsto avoid cracking of the hydrocarbon.

It is noted that the carburation of a mixed hydroxide or oxideaccompanied by reduction of one of the metallic elements to the metallicstate according to the method according to the invention is easier thana carburation of a simple oxide, always better ciystallized, hence lessreactive. This is particularly established in the case of thecarburation of titanium in the presence, for example, of iron, of nickelor of cobalt: the carbide TiC is then formed between 800 and 1000 C.whilst it is impossible to obtain in this range of temperature whenthere is subjected to the action of the hydrogen-methane mixture, thehydroxide Ti(OH) or the oxide TiO The dispersions according to theinvention, prepared by means of the abovesaid method, can be used forthe practicing of conventional technics of powder metallurgy, bysubjecting them to sintering either as they are, or after having mixedthem with a powder of the second metal if the proportion of carbide mustbe reduced in the final material.

In order that the invention may be more fully understood, variousexamples of the method and products according to the invention aredescribed below, purely by way of non-limiting illustration.

EXAMPLE 1 In order to prepare a dispersion of chromium carbide in ironcontaining 95% by weight of iron, one commences by preparing the mixedoxalic complex obtained by syncrystallization of the complex oxalates ofeach of the two metals.

The product thus obtained is subjected to selective carburation bybringing its temperature to 900 C. at the speed of 250 C./h. in agaseous current distributed by a mixing metering pump and constituted byhydrogen (21.80 l./h.) and by methane (0.44 l./h.), i.e. containing 2%of methane. After 18 hours of maintenance at 900 C. in the atmosphereconsidered, it is observed by radiocrystallographic analysis that theproduct obtained is twophase and contains also orthorhombic chromiumcarbide Cr C finely dispersed in the a iron. This product has the formof a fine grey powder.

EXAMPLE 2 In order to prepare a dispersion of chromium carbide in iron,containing 60% by weight of iron, one starts by preparing the mixedoxalic complex of the desired composition as indicated in Example 1.

The product thus obtained is subjected to carburation at 900 C. underconditions of temperature and gaseous fiow given in Example 2. After 16hours of maintenance at 900 C. in the atmosphere considered,radiocrystallographic analysis reveals the presence of a hexagonalsingle carbide Cr Cr dispersed in the or iron.

EXAMPLE 3 In order to prepare a dispersion of titanium carbide incobalt, containing 70% by weight of cobalt, one starts by preparing aco-precipitate of hydrated oxides, in the following manner: there isadded simultaneously, but separately and drop by drop, an aqueoussolution of 69.1 g. of cobalt nitrate Co(No 6H O and 23.2 g. of titanylsulfate TiOSO 4H O and a three times normal solution of soda in aboutone litre of water stirred vigorously in a Pyrex reactor of two litrescapacity. The simultaneous precipitation of the two hydroxides takesplace drop by drop; the very fine precipitated obtained is filtered,washed with boiling water until disappearance of sulfate and sodiumions, and dried for 20 hours in the oven at 110 C.

The product thus obtained, finely ground, is subjected to simultaneousreduction and carburation by bringing its temperature to 800 C. at thespeed of 250 C./h. in a gaseous current constituted of hydrogen (21.80l./h.) and of methane (1.15 l./h.), i.e. containing 5% of methane. Afteri16 hours of maintenance in the atmosphere considered,radiocrystallographic analysis confirms the obtaining of a finedispersion of titanium carbide TiC in cubic 18 cobalt. The titaniumcarbide thus obtained at i3 00 C. is fine grained, as shown by the widediffraction mes.

4 EXAMPLE 4 In order to prepare a dispersion of titanium carbide innickel, containing 90% by weight of nickel, one starts by preparing theco-precipitate of the two hydrated oxides according to the method ofoperation described in Example 3, by using a saline solution of nickelnitrate and titanyl sulfate.

The compound thus obtained is subjected to simultaneous reduction andcarburation by bringing its temperature to 880 C. in a gaseous currentconstituted by hydrogen (21.80 l./h.) and methane (0.56 l./h.)containing 2.5% of methane. After 16 hours of maintenance in theatmosphere concerned, there is obtained a fine dispersion of the carbideTiC in metallic nickel.

EMMPLE 5 In order to prepare a dispersion of vanadium carbide in cobalt,containing by weight of cobalt, one starts by preparing theco-precipitate of the two hydrated oxides according to the method ofoperation described in Example 3, by making a precipitation from asaline solution of cobalt nitrate and vanadyl sulfate with a -solutionof commercial ammonia three times diluted. The precipitation havingtaken place, it is brought to boiling to restore it to pH 7 and todestroy the vanadate which could have formed.

The compound thus obtained is subjected to simultaneous reduction andcarburation by bringing its temperature to 800 C. in a gaseous currentof hydrogen (21.80 l./h.) and of methane (1.15 l./h.), i.e. containing5% of methane. After 14 hours of maintenance at 800 C. in the atmosphereconsidered, there is obtained a fine dispersion of vanadium carbide VCin cubic p cobalt.

EXAMPLE 6 In order to prepare a dispersion of vanadium carbide in iron,containing 80% by weight of iron, one starts by preparing theco-precipitate of the two hydrated oxides according to the operationalmethod described in Example 3, by precipitating from a saline solutionof ferric nitrate and vanadyl sulfate with a commercial solution ofammonia diluted three times.

The compound thus obtained is subjected to a simultaneous reduction andcarburation by bringing its temperature to 920 C. in a gaseous currentof hydrogen (21.80 l./h.) and methane (0.44 l./h.), i.e. containing 2%of methane.

After 20 hours of maintenance at 920 C., radiocrystallographic analysisshows the presence of very little or iron, of cementite Fe C and ofcubic vanadium carbide VC. Baking of the preceding product underhydrogen (15 l./h. approximately) enables the cementite to be destroyedand there is obtained after 14 hours of baking at 920 C. or iron, verylittle Fe C and the carbide VC finely dispersed. A further baking for 13h. at 920 C. under hydrogen then leads to the desired product, adispersion of vanadium carbide in the or iron.

EXAMPLE 7 In order to prepare a dispersion of niobium carbide in iron,containing 70% by weight of iron, one starts by preparing an intimatemixture obtained by co-evaporation of the complex oxalates (NH [Fe(C Oand 4)3[ 2 4)3]- The mixture thus obtained is subjected to asimultaneous reduction and carburation by bringing its temperature to900 C. in a gaseous current of hydrogen (21.80 l./h.) and of methane(0.44 l./h.), i.e. containing 2% of methane. After 15 hours ofmaintenance at 900 C., there is obtained a dispersion of NbC carbide in0: H011.

EXAMPLE 8 In order to prepare a dispersion of a solid solution oftitanium carbides and of tantalum in cobalt, containing 90% by weight ofcobalt, one starts by preparing an intimate mixture obtained byco-evaporation of the oxalates a o 4)z[TiO( a 4)2] a d in suitableproportions, and corresponding to the atomic ratio Ti/Ta=1. I

The compound thus obtained is subjected to simultaneous reduction andcarburation by bringing its temperature to 950 C. in a gaseous currentof hydrogen (21.50 l./h.) and of methane (0.44 l./h.), i.e. containing2% of methane. After 15 hours of maintenance at 950 C. in the atmosphereconsidered, radiocrystallographic analysis indicates the presence of thesolid solution of the carbides TiC and TaC dispersed in a mixture ofhexagonal a cobalt and of cubic B cobalt.

EXAMPLE '9 In order to prepare a dispersion of a solid solution ofcarbides of titanium and of niobium in iron, containing 80% by weight ofiron, one starts by preparing an intimate mixture obtained byco-evaporation of the oxalates (NH4)3[FE(C2O4)3], and (NH [NbO(C O insuitable proportions and corresponding to the atomic ratio Ti/Nb-=1;

The compound thus obtained is subjected to simultaneous reduction andcarburation by bringing its temperature to 1050 C. in a gaseous currentof hydrogen (21.80 l./h.) and of methane (0.22 l./h.), i.e. containing1% of methane. After 15 hours of maintenance at 1050 C. in theatmosphere considered, radiocrystallographic analysis indicates thepresence of the solid solution of TiC and NbC carbides, dispersed in oniron EXAMPLE 10 In order to prepare a dispersion of chromium carbide CrC in copper, containing 60% by weight of copper, one starts by preparingthe starting compound i.e. an intimate mixture obtained byco-evaporation of a solution of the citrates of copper and of chromium.This solution is obtained by heating under reflux, for two hours, anaqueous solution of diamrnonium citrate in excess to which there isadded copper powder, chromic anhydride CrO and a little oxygenatedwater. It is filtered to eliminate the last traces of copper notattacked, and the filtrate is evaporated on a sand bath.

The compound thus obtained, finely ground, is first subjected tooxidation in air, for 12 hours at 660 C., which leads to an intimatemixture of cupric oxide CuO and of cupric chromite CuCr O This mixture,finely ground, is then subjected to simultaneous reduction andcarburation, by bringing its temperature to 1000" C. in a gaseouscurrent of hydrogen (21.50 l./h.) and of methane (0.22 l./h.) i.e.containing 1% of methane. After 15 hours of maintenance at 1000 C. inthe atmosphere considered, radiocrystallographic analysis confirms theobtaining of a dispersion of chromium carbide Cr C in copper.

IEXAMPLE 11 In order to prepare a ferronickel alloy with 48% by weightof iron and 52% of nickel, containing 3% by weight of vanadium carbidefinely dispersed, one commences by preparing the starting product, i.e.a coprecipitate of the three hydrated oxides according to the method ofoperation described in the Example 3, by making a starting precipitationfrom a saline solution of ferric nitrate, of nickel chloride and ofvanadyl sulfate with 25% ammonia, operating at pH 7.5.

The compound thus obtained is subjected to simultaneous reduction andcarburation by bringing its temperature to 950 C. in a gaseous currentof hydrogen (21.80 l./h.) and of methane (0.44 l./h.) i.e. containing 2%of methane After 15 hours of maintenance at this temperature in theatmosphere considered, radiocrystallographic analysis shows that therehas been obtained a 6 dispersion of vanadium carbide VC in theferronickel of cubic structure with centered faces, approximating to 7iron, of parameter 0:3.5'85 A.

EXAMPLE 12 In order to prepare a dispersion of 3% by weight of titaniumcarbide in a nickel-cobalt alloy of composition by weight Ni-10% Co, onestarts by preparing the co-precipitate of the three hydrated oxidesaccording to the method of operating described in Example 3, byeffecting a precipitation from a saline solution of the chlorides ofnickel and cobalt and of titanyl sulfate in suitable proportions, withthree times normal soda.

The compound thus obtained is subjected to simultaneous reduction andcarburation by bringing its temperature to 1020 C. in a gaseous currentof hydrogen (21:80 l./h.) and of methane (0.22 l./h.) i.e. containing 1%of methane. After 16 hours of maintenance at 1020 C. in the atmosphereconsidered, radiocrystallographic analysis confirms the obtaining of anickel-B cobalt alloy of center faced cubic structure, very close tothat of nickel, containing a dispersion of titanium carbide TiC.

EXAMPLE 13 In order to prepare a refractory composition based ontitanium carbide, containing 6% by weight of cobalt usable as binderphase in sintering, one starts by preparing a co-precipitate of the twohydrated oxides according to the operational method described in Example3, by effecting a precipitation from an aqueous solution of titanylsulfate and of cobalt chloride in suitable proportions, with 25%ammonia. During the whole of the operation the pH must not exceed 8.

The compound thus obtained is subjected to simultaneous reduction andcarburation by bringing its tem perature to 1030 C. in a current ofhydrogen (21.80 l./h.) and of methane (0.22 l./h.) i.e. containing 1% ofmethane. After 20 hours of maintenance at 1030 C. in the atmosphereconsidered and cooling, there is obtained a grey-black powder.Radiocrystallographic analysis confirms the presence of titanium carbideTiC and of a binding phase of center faced cubic fi-cobalt.

As is self-evident, the invention is in no way limited to those of itsmethods of application, nor to those of its methods of production of itsvarious parts, which have been more particularly indicated; it embraces,on the contrary, all variations.

We claim:

1. Process of preparing a dispersion of at least one carbide in ametallic base, said carbide being in the form of particles distributeduniformly in the midst of elementary grains of said base comprisingsubjecting at least one first metal from which the carbide is to befor-med selected from the group consisting of Ti, V, Nb, Ta and Cr, andat least one second metal selected from the group consisting of Fe, Co,Ni, Cu, Zn, Cd, Ag, Sn, Pb, Bi, Ge and Tl, said metals being in the formof a coprecipitate of hydroxides or a mixed complex thereof in anatmosphere of hydrogen and hydrocarbon to a temperature sufficient topermit simultaneous reduction and carbidization of said coprecipitate ormixed complex and less than 1100 C., for a time sufiicient to achievethe reduction of all the oxides and the carbidization of said firstmetal.

2. Method according to claim 1, wherein said metal of the dispersion isan alloy.

3. Method according to claim 1, wherein said hydrocarbon is methane.

4. Method according to claim 1, wherein the heating is effected at aspeed of the order of to 400 C./hour.

5. Method according to claim 1, wherein that the step of simultaneousreduction and carburation is effected in a fixed bed.

6. Method according to claim 1, wherein the step of simultaneousreduction and carburation is effected in a fluidized bed.

7. Method according to claim 5, wherein the duration of the step ofsimultaneous reduction and carburation is of the order of 10 to 20hours.

8. Method according to claim 1, wherein the proportions of hydrogen andof hydrocarbon of the atmosphere used during the step of simultaneousreduction and carburation are respectively of the order of 99 to 90 and1 to 10%. l

9. Method according to claim 1, wherein the carbide of the second metalis stable under the conditions of simultaneous carburation andreduction, and said step is followed by a supplementary treatment ofreduction in pure hydrogen at the same temperature for a time sufiicientto completely reduce the carbide of said second metal.

References Cited UNITED STATES PATENTS WAYLAND W. iSTALLARD, PrimaryExaminer

